This is a further development of the snap fasteners shown in U.S. Pat. Nos. 4,409,706, 4,577,376, 4,646,399 and U.S. application Ser. No. 07/382,666, filed Jun. 29, 1989, now U.S. Pat. No. 5,050,279, all of which are incorporated herein by reference. While the stud design disclosed in application Ser. No. 382,666 represents a satisfactory, operable design, field testing showed that variation in the inside diameter of the grommet aperture resulted in fasteners where the grommet and stud could not be readily snapped together or disconnected to fasteners where the grommet and stud were so loosely joined that they might easily and inadvertently separate. The variations in aperture diameter in the grommet were traced to two major causes: (1) the manner in which the artisan assembled the grommets to the fabric and (2) in use the grommets were being distorted beyond their elastic limit.
Various design changes were experimented with in an effort to provide a grommet with a reliable inside diameter and as shown in application Ser. No. 382,666 grommets with an internal ring incorporated therein were proposed. The following U.S. and foreign references were known and considered:
______________________________________ U.S. Pat. Nos.: Foregin Patents: ______________________________________ 506,110 French Patent No. 450,924 681,086 British Patent No. 872,204 717,333 German Patent No. 98,040 991,156 Austrian Patent No. 91,282 1,096,897 Swiss Patent No. 80,821 1,204,173 1,302,918 1,652,139 2,099,979 2,328,016 2,709,290 2,807,069 2,895,199 ______________________________________
I finally determined that the portion of the fastener to be snapped on the stud (hereinafter the retainer) had to have an aperture whose diameter was independent of the manner in which the fastener was attached to the fabric, and would not be distorted beyond its elastic limit when applied to or removed from the stud. I further determined that both the stud and the retainer should be made of plastic which could not corrode when exposed to corrosive environments and whose tolerances could be closely held.
Consideration was given to methods of attaching the retainer to the fabric including heat sealing as in U.S. Pat. No. 2,895,199, or gluing, or where the fabric was mechanically held as in U.S. Pat. No. 2,807,069. Each of these approaches held a variety of disadvantages.
An important consideration was ease of attachment of the fastener to the fabric material. Ideally the retainer should be attachable in a quick and simple fashion either manually using conventional tools or with setting tools usable in existing presses.
Similarly, the studs should be attachable to the fabric using conventional fasteners--where a fabric to fabric connection was desired, without the need for special adapters or modifications of the stud.
I determined the fastener should be so constructed that when assembled the plastic parts would be protected from the weather. While plastic materials might be selected containing ultraviolet inhibitors and good resistance to moisture, if the design was such that the plastic parts were substantially covered or shielded from the weather, the parts should function reliably and be aesthetically pleasing for a greater period of time.
Finally, I decided no hole should be required through the fabric for reception of the stud, as is required in the case of other commercially available fasteners such as the LIFT A DOT.RTM. fastener manufactured by TRW or the twist type fastener manufactured by RAU Fasteners, Inc. of Providence, R.I. so that the fabric would not be weakened at the connection and would maintain maximum tear strength and integrity.